Not sure if this is official, but i've made some adjustments on the URL to "activate" Bookings on my Office 365 Tenant. I've tested with an Enterprise E5 trial tenant this adjustment and it was successful to use Bookings. Enter in this URL to start using Bookings: https://outlook.office.com/owa/?path=/bookings

Mudasar, I was able to set up bookings using the iOS app and now I have access. As stated below, you can use the following link to access it under your E3 subscription once you set it up on the mobile app.

Except that "Business Apps (Free)" isn't listed as an option to add to our subscriptions, so still can't assign to users to add the app icon to their launcher (direct URL method above still works fine though).